Scanning Probes
Scanning probes are non-contact optical probes for measuring thousands of points a second on the 3D surface shape of an object. There are three broad types of scanning probe: point, stripe and area. This invention concerns stripe scanning probes. Most stripe scanning probes use the principal of optical triangulation. Stripe scanning probes are provided or are being developed by Metris (Belgium), 3D Scanners (UK), Romer (France), Faro Technologies (USA), Perceptron (USA), Steinbichler (Germany), Pulstec (Japan), Micro Epsilon (Germany), SICK IVP (Germany), Vitana (Canada), Laser Design (USA), Datapixel (Spain), Optimet (Israel) and Kreon (France) amongst others.
Movement of Stripe Scanning Probes
In order to scan the surface of an object a stripe scanning probe needs to move over the object's surface in a similar way to how a paintbrush is used for painting a surface. The movement of the stripe scanning probe may be accomplished manually or by automated equipment.
Localisers for Stripe Scanning Probes
In order to get accurate data of the surface of an object, a localiser is required to register the position and orientation of the stripe scanning probe when surface data is captured by the stripe scanning probe. Localisers are generally mechanical or remote. Localisers may also have the dual functionality of supporting/moving the probe as well as supplying its position and orientation. Mechanical localisers include: 3-axis Cartesian coordinate measurement machines (CMMs), Manual CMM arms, Robot CMM arms and essentially all types of combinations of continuous mechanical linkages that might accurately register the position and orientation of a probe end relative to a base end, the stripe scanning probe being rigidly attached to the probe end. Remote localisers include: optical trackers, optical CMMs, magnetic trackers and GPS systems. Remote localisers often require one or more lines of sight between the stripe scanning probe and the remote localiser equipment.
Since the 1970's, companies have been building manually operable CMM arms that have recently achieved a measuring accuracy using a contact probe of between 0.025 mm (+/−2 Sigma) and 0.005 mm (+/−2 Sigma) depending, mainly, on the reach of the Manual CMM Arm, Manual CMM Arms are expected to become more accurate with further development. These Manual CMM Arms are now accurate enough for many measurement requirements and area growing sector in the measurement marketplace. They have the flexibility of being able to get into areas with difficult access. Manual CMM Arms are acceptably accurate for many applications, but are not automated; they are expensive to operate, particularly since a semi-skilled operator is required; human operators are also subject to human error. Manual CMM Arms are provided by companies including: Hexagon Cimcore (USA), Faro Technologies (USA), Hexagon Romer (France), Zett Mess Technik (Germany) and Tokyo Boeki (Japan). As examples, U.S. Pat. No. 3,994,798 Eaton, U.S. Pat. No. 5,402,582 Raab assigned to Faro Technologies, U.S. Pat. No. 5,829,148 Eaton and U.S. Pat. No. 6,366,831 Raab assigned to Faro Technologies disclose background information on Manual CMM Arms.
Stripe Scanning Probes on Manual CMM Arms
Stripe scanning probes on Manual CMM Arms were disclosed by Crampton, an inventor of the present invention, in several patent applications including PCT/GB96/01868. Stripe scanning probes for Manual CMM Arms are provided or are being developed by Metris, 3D Scanners, Romer, Faro Technologies, Perceptron, Steinbichler, Pulstec and Kreon amongst others. As yet, a measurement accuracy standard does not exist that defines the way accuracy should be measured for Stripe scanning probes. The marketplace is in the situation of not being able to perform standard tests to verify accuracy and enable comparison between stripe scanning probe types in a practical way. Stripe scanning probes have become accurate, largely because their measuring range is short. In general, stripe scanning probes gather measurement data over a measuring range of the order of 20-400 mm. This is often at a standoff to the end of the Manual CMM Arm. The accuracy of the best Manual CMM Arms combined with the best Stripe scanning probes is already better than 0.050 mm (+/−2 Sigma) and can be better than 0.010 mm (+/−2 Sigma) for short measuring ranges. Stripe scanning probes are generally mounted offset on the side of the Manual CMM Arm or mounted on the probe end of it. Stripe scanning probes are usually quickly dismountable from a Manual CMM Arm using a mounting system that is mechanically repeatable to an acceptable degree of accuracy.
Robot CMM Arms and their use with stripe scanning probes were disclosed by Crampton, an inventor of the present invention, in several patent applications including PCT/GB2004/001827, Robot CMM Arms have the advantage over Manual CMM Arms of supporting and moving the stripe scanning probe automatically. Both Manual CMM Arms and Robot CMM Arms have the advantage over Cartesian CMMs of articulation.
Market Needs
Accuracy: Users demand ever higher accuracy and data quality from their stripe scanning probes.
Speed: When surfaces are scanned, they are sampled. The quality and automation of the surface reconstruction or measurement is related to the number and density of raw points scanned. Scanning rates of current sensors on the market are typically 3,000 to 20,000 points per second. Rates exceeding 200,000 points per second will increase the productivity of the stripe scanning probes by reducing both data capture time and manual intervention in the post-processing activity.
Cabling: a stripe scanning probe with fewer cables has higher utility than a stripe scanning probe with lots of cables. Cables are an ever increasing proportion of the cost of CMMs.
Compactness: it is desirable to provide a stripe scanning probe with built in processing and without an extra box of electronics and associated cables.
Cost: the market place is becoming more competitive and reductions in cabling, components are desirable to reduce the manufacturing cost of stripe scanning probes.
Current Situation
The vast majority of stripe scanning probes on the market are analogue and use video CCD imaging sensors. This state of the art imaging technology has limited the accuracies, data quality, speeds, cost and compactness of the solutions.